The term ‘Smart’ (or ‘Intelligent’) when associated with battery chargers is used widely and loosely so it is important to understand what a Smart Charger can be versus what it is you are actually looking at.
In this article we’ll cover all the features a Smart Charger can include but always bear in mind any particular product may only contain one or a few of these and still bear the ‘smart’ label.
Let’s start with a short summary of all the capabilities a Smart charger can have before looking at each one in more detail:
- Reverse Polarity Check – to avoid the charger being incorrectly connected
- Battery Type detector – to detect what type of battery they are connected to – Lead Acid, Lithium, etc.
- Battery health check – to see if the battery can be charged or has reached the end of its life
- Short circuit sensor – to avoid trying to charge batteries where one or more of the cells have shorted out.
- Battery recovery operations – to attempt to recover batteries that appear to have died
- Charging speed control – to allow faster charging when possible
- Fast charging assistance – features to increase the rate of recharge
- Full charge cut off – to stop passing a current through a battery when it has reached full charge
- Maintenance mode – periodical topping up of the battery charge as needed over time
- Continuous connection mode – when the charger is connected for long periods of time it can change the state of charge to a lower level than 100% to increase long term battery life.(“Winter charging”)
- Low voltage protection – cutting the battery off from the appliance to stop it over discharging
- BMS communication – communicating with the Management System of the battery
- Safety monitoring – such as monitoring the battery temperature, spikes in current, etc
- Time awareness – on order to, for example, only charge at times when electricity is cheaper
- Grid interaction – communication with the mains power grid to, for example, prioritize using green energy
- Multi-Source power integration – prioritizing, for example, electricity from a households solar panels over electricity from the mains grid.
- Charger management system interface – connecting the charger, via WiFi or Bluetooth, to smartphone or desktop apps with various capabilities to monitor and/or control the charger.
Reverse Polarity Check
For a rechargeable battery to charge an electrical current needs to be passed through it via the positive and negative terminals.
A battery charger will have two connections, one for the positive terminal and one for the negative terminal of the battery.
In most consumer products, such as laptops and smartphones, the charger connections are designed in such a way that it is not possible to connect the charger incorrectly. However some batteries and chargers are open to human error, it is possible to connect the charger to the battery incorrectly.
If the battery has very little charge left in it then the electrical current from the charger will start to push through the battery in a way it is not designed for. The resulting heat from this friction can result in an explosion or fire.
But if the battery is close to 100% discharge it is possible that the charge will work resulting in reverse polarity. This is where the negative terminal becomes positive and the positive terminal becomes negative. Connecting such a battery to a device might damage the device or cause the battery to short out.
If the battery is still partly charged when the charge is connected incorrectly the current will be pushed back and the charger will sustain damage. This may simply be a blown fuse but potentially the damage to the charger might be enough to destroy it completely.
In order to avoid any of the above happening a smart charger with a reverse polarity check has the ability to sense if it has been incorrectly connected to a battery and, if so, break the connection via an internal circuit.
This protects both the charger and battery from potential damage and avoids any risk of fire or explosion.
Battery Type Detector
The main types of rechargeable batteries are Lithium, Nicad, Nickel and Lead Acid. Their charging needs vary.
Attempting to charge a lead acid battery, for example, at the same rate as a lithium battery might well result in damage to the battery in the best scenario and a fire or explosion in the worst.
On the other hand charging a lithium battery at the same rate as a lead acid battery makes the process far slower than it needs to be, wasting time and the opportunity to use the device.
Traditionally this has meant users needed different chargers for each battery type. Even within a type different chargers may have been needed for different voltages so a user would need one charger for their 12 volt lead acid battery and a alternative one for their 6 volt lead acid battery.
Some Smart Chargers are now able to identify the battery type and voltage when they are connected through two steps.
The first step is to read the voltage of the battery. The voltage of a battery reduces gradually as it is discharged so it is an indicator of how much charge the battery contains.
A fully charged 12 volt lead acid battery will have a voltage of up to 13 volts and 11.5 volts when fully discharged whereas a discharged 6 volt lead acid battery will have a voltage of between 6.5 and 5.8 volts depending on its state of charge.
So if the voltage lies anywhere between 13 and 11.5 volts the charger can be confident it is dealing with a 12 volt battery rather than a 6 volt battery.
The next step is to apply a small current that would be safe for all battery types and monitor how quickly the voltage rises. A slow rise indicates a lead acid battery that will require a gradual rate of recharge. A quick rise will indicate other battery types, such as Lithium, which can be recharged more rapidly.
The rate of voltage changes as the battery recharges then give more indications of whether the battery is Lithium, Nicad or Nickel allowing the charger to then alter the charge current further.
Battery Health Check
Once a charger is correctly connected and, if the charger has the feature, the battery type is identified the next question is – can this battery be recharged?
Reasons why a battery can be charged include that it is already fully charged, it is faulty or it has reached the end of its life.
All batteries have a limited service life because the internal components and materials gradually degrade over time whether in use or not. A typical lead acid battery, for example, will last about 3-5 years while lithium batteries will last for 3,000 to 5,000 discharge and recharge cycles.
A traditional battery charger will simply pass a small charge through a battery in order to recharge it even if the battery has reached the end of its life span and can no longer take a charge. A smart charger will look to see if the battery is chargeable using State of Charge as a measurement
As mentioned earlier the State of Charge of a battery can be determined by measuring the voltage of the battery. In the graph below we can see a 12 volt battery actually has a voltage of close to 13 when fully charged and less than 11 when fully discharged.
This is only a very basic measure. Every battery that comes off a production line has very slight variations due to the manufacturing process so one 12 volt battery may have a voltage of 13 volts when fully charged while another might have 12.7 volts, even when comparing batteries from the same brand.
However the one thing we know for sure is that as a battery recharges it’s voltage will increase and this increase will start as soon as a charger starts to pass a current through the battery.
Some smart chargers will look to see if it senses this increase and, if there is none, can signal to the user that the battery is no longer rechargeable.
Despite this feature it should be noted that smart chargers can get this wrong. If a battery has recently been heavily discharged it will probably be quite hot internally and in this situation it will not be able to take a charge before cooling.
If it is a smart battery able to communicate with the charger then the charger will be able to take this into account. Otherwise the charger simply senses no change in voltage and reports the battery as ‘unchargeable’.
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As such, if you are not using a smart battery with compatible smart charger, always let batteries that have been in heavy use cool off for a while before connecting a charger.
In the video below we can see the test taking place before the charging starts.
VIDEO OF CHARGER BEING PLUGGED IN
Short Circuit Sensor
Most batteries are actually made up of smaller batteries, known as ‘cells’.
A 6 volt lead acid battery contains three 2 volt cells connected together in such a way to provide 6 volts via the positive and negative terminals.
In the image below we can see a 6 volt lead acid battery with the lid off revealing the three cells.
If any of these individual cells have failed it may still be possible to apply a charge to the battery but there won’t be much point. A 6 volt battery with a failed 2 volt cell will give, even when fully charged, 4 volts. That’s not enough to power a device which needs 6 volts.
A smart charger will be able to check this by taking a voltage reading. A fully discharged 12 volt lead acid battery will have around 11 volts. Anything below that signals a failed cell.
Cell failure can occur simply because a battery is worn out but it is also possible a cell can fail due to a manufacturing error or over charging and/or discharging which can cause internal components to warp and short out.
If the battery is a Smart Battery and you are using a compatible Smart Charger the battery will report this to the charger removing some of the guess work and letting the user know, more accurately, why the battery cannot be charged.
Battery Recovery Operations
Just because a battery cannot take a charge or it appears that one or more cells are faulty doesn’t mean a battery has reached the end of its life. It can be possible to recover the battery to a state where it can take a charge.
The most common situation is with lead acid batteries that have not been used for a long period. This type of battery often suffers from ‘sulfation’. This is where crystals build up on internal elements of the battery which stop the free movement of electrons needed for recharging.
Sulfation can sometimes be repaired by pulsing an electric current through the battery. The pulses gradually break down the crystals so the electrons can move again.
A smart charger that senses a battery unable to charge or with what appears to be a faulty cell might try and operation like this to see if it resolves the issue.
Charging speed control
Simple battery chargers pass a constant current through a battery but its a lost opportunity as batteries with a high state of discharge are able to take a much higher current to begin with. This can dramatically reduce the time it takes to recharge a battery.
To understand why this is we need to look inside a battery cell. The image below is a sealed lead acid battery with 3 cells
The plates from one cell have been pulled upwards revealing two rows containing 3 pairs of plates. The number or rows and number of plates may vary in different batteries.
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Each plate in a pair is constructed using different materials, although they can look visually very similar. These are referred to as the Anode and the Cathode plates.
Note a cell can contain just one pair if plates and these are often found in cylindrical batteries where the pair of plates are wound into a coil or in lithium batteries where they are folded into various shapes.
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For now we’ll use lead acid as an example because it is easier to demonstrate what is happening but the principle is the same, no matter the chemistry or shape of the battery.
The plates are kept apart by a separator (shown in the image above as a white cotton type of material but again the exact material may vary). This is needed to stop the plates touching each other which would cause the battery to short out and die.
In the next image we are zooming in on a pair of plates with the separator removed.
In a discharged battery all the electrons will be on the Cathode plate. In the image below the electrons, shown as blue balls, are sized for demonstrative purpose. In reality electrons are so small you cannot see them with the naked eye.
The aim of recharging is to move the electrons back to the Anode plate.
When the charger passes an electrical current through the cell the electrons gradually break off from the cathode and move towards the anode. However they don’t move in a straight line, they float, bob, jostle and wobble through an electrolyte chemical which fills the cell between the plates.
The first electrons to arrive at the anode find plenty of free space and attach easily but the more the anode is filled, the harder it is for the remaining electrons to find a free space. They just keep colliding with other electrons already attached to the wall.
This is why even non-smart chargers slow down the charge towards the end of the recharge process.
A smarter way to charge, however, would be to apply a higher current at the beginning when the electrons can easily find a space on the anode.
But if we keep this higher power setting later it causes higher and faster collisions between electrons looking for free space.
These collisions result in a build up of heat which could damage the battery or cause a fire or explosion.
Some smart chargers will sense the state of charge of a battery and apply a varying level of current. Higher current when the battery is highly discharged and easing off as full charge approaches.
When a compatible smart charger and smart battery are connected they can optimize this even further. A smart battery can report it’s internal temperature to the charger which will allow the charger to know what maximum current can be applied at any moment in time to give the highest level of charge without damaging the battery or risking explosion or fire.
As a side note some Smart Batteries have internal systems that manage this charging process. The smart battery makes the decision on how much charge to accept at any point in time and draws the appropriate amount of current from the charger.
Fast Charging Assistance
As we saw in the previous section one of the main obstacles to really fast charging is the build up of heat caused by electrons colliding with each other as they move from the cathode to the anode.
A simple solution to this, where space allows, is to include a way to cool the battery as it is charging.
Some smart battery and charger combos, as seen in the video below, are designed to work this way. The charger includes a fan to blow cool air and the battery is designed so that this cool air can move through channels and help lower the temperature of internal components.
VIDEO OF SMART CHARGER WITH AIR COOLING
In large industrial settings a charger may also control the temperature of an entire room or localized cooling systems (both air and liquid based), used as needed if rapid recharging is required.
Full charge cut off
Once a battery is fully charged the energy from the charger has no where to go and ends up causing damage to the battery. This is known as ‘overcharging‘.
Only the most basic of battery chargers do this. Even fairly simple ones know to switch off if the battery reaches full charge. But how do they know?
As we saw in the section above ‘Battery Health Check’, as a battery charges its voltage increases. A fully discharged 12 volt battery may have a voltage of 11.5 volts. As it charges this increases gradually to around 12.6 volts.
However the exact voltage at full charge will differ slightly, even for 12 volt batteries from the same manufacturer. So a simple cut off at X volts is not possible.
A smart charger will simply stop once it senses the voltage is no longer increasing and so avoid over charging.
Maintenance Mode
Most battery chargers work through 4 stages – test, charge, absorption (abs) and maintain – as demonstrated in the graph below.
The graph is to demonstrate the first 3 steps. In reality the testing phase usually takes seconds while the charge phase can take one or more hours.
The graph also shows the ‘bulk charge’ phase as constant but as we have already seen above a Smart Charger may vary this rate. The gradual decline in the charging rate as the battery nears full charge is because of the difficulties in charging at this moment that were discussed above in the section ‘Charging Speed Control‘. Again this may not be a smooth curve and will decline at varying rates depending on what the Smart Charger senses.
In the video below we can see a smart charger being turned on, carrying out a test and then beginning a charge using air cooling to optimize the rate of charge.
VIDEO OF BATTERY CHARGER TURNING ON
Once a battery is fully charged a traditional charger will continue to pass a very small current through the battery known as a ‘trickle charge’ to keep it fully charged.
Some Smart Chargers will switch off the current and then perform regular checks to see if the battery needs a further recharge which is better for the battery compared to the ‘trickle charge’.
This feature is often used when a battery is going to be stored for a long period of time, such as batteries in vehicles that are not going to be used for several weeks.
However, although some consider this ‘Smart’, it is the most basic form of handling battery storage. More advanced chargers use more comprehensive approaches as covered in the section below.
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Continuous Connection Mode
There are times when we need to, or it is practical to, keep a charger connected to a battery over a long period of time.
Two common examples are batteries for garden machinery during the winter and batteries for mobile internet routers which are plugged in most of the time.
But this is not always a case of keeping a battery ‘fully charged’. Lead acid batteries will have the longest lifespan when they are kept at around 70% charge. Lithium batteries, on the other hand, are best kept at 40 to 70% charged.
A smart charger can take this into account. If it senses it has been connected to a battery for a long time it can top up, or even discharge, a battery as needed to achieve an optimized long term State of Charge for a better battery lifespan.
This feature is also often referred to as ‘Battery Charger Protection Mode‘.
The image below shows a WiFi rooter with an internal charger that has this feature. The full message at the bottom of the screen reads, “Battery will be limited to 65% charge when on left on charge for more than 16 hours”
The level of complexity that smart chargers offer to achieve this varies. For example a 6 volt lead acid battery at 70% charge actually has a voltage of around 6.2 volts. A smart charger may simply aim for this level when in maintenance mode.
However as we have seen earlier the voltage of a battery is only a rough indicator of its state of charge. A fully charged 6 volt lead acid battery might have a voltage anywhere between 6.2 volts and 6.5 volts. This is true even for the same battery from the same manufacturer due to variations in the production process.
So simply keeping a lead acid battery at 6.2 volts might work for one battery but be too high a long term charge for another.
A full smart charger will fully charge a battery, record the voltage at that point, and then calculate the best voltage for long term charging. It may then simply let the battery gradually discharge to this point (as even batteries not in use will self-discharge over time) or it may actively discharge the battery to the required State of Charge.
It’s worth noting the Maintenance mode function can sometimes be built into a Smart Battery rather than the Smart Charger.
Low Voltage Protection
While all batteries can be fully discharged this causes damage to the internal components and shortens the battery’s overall lifespan.
For the longest service life Lead Acid batteries should not discharge more than 30% while lithium batteries should not go below 40%.
Where a battery is often connected continuously to a charger, such as a laptop used mainly as a desktop, the charger may also be tasked with ensuring the battery does not discharge too low.
The charger takes this role because it is monitoring the battery voltage anyway and using this data to provide a charge as needed.
Theoretically this should mean the voltage always stays near full charge but if for some reason the battery stops being able to take a charge then it could fully discharge.
As such the charger may disconnect the battery from the device if the voltage falls below a certain level to avoid damage from full discharge.
In other scenarios, where the charger is not connected most of the time, the low voltage protection role may fall to the battery itself (if it is a Smart Battery) or a separate protection circuit.
BMS Communication
Many Smart Batteries contain a Battery Management System (BMS). These vary in complexity but can include:
- The date the battery was manufactured
- How often the battery has been discharged and recharged (cycled)
- The expected lifespan of the battery
- The current internal temperature of the battery cells
- The exact state of charge of each cell (where the battery is made of more than one cell)
A compatible Smart Charger will be able to read all of this data in real time to provide optimized charging. A battery, for example, that is cool inside can be charged faster than one that is hot because of recent use.
Safety Monitoring
In its basic form a Smart charger may be able to monitor issues with the batteries such as spikes in current which could indicate a faulty cell.
If the charger is communicating with the battery’s management system it can also be aware of other changes such as a high internal temperature of the cells that, if not dealt with, could lead to fire or an explosion.
Some smart chargers can then apply measures such as fan cooling or disconnecting the battery from external devices until the situation has normalized.
Time Awareness
Some regions of the world offer different prices for electricity based on the time of day. Tapping into these cheaper rates can significantly decrease the cost of recharging batteries, especially when the recharge is not urgent.
This might be ideal, for example, for households that use battery power during the day and evening. Cheaper electricity tariffs available at night can then be used to recharge the batteries.
Such chargers can either be programmed with their own internal clocks or be connected to the internet via a Wi-Fi router to set the current time.
Grid Interaction
The next step up from time awareness is full interaction with the electricity grid via the internet. The smart charger connects with the electricity provider and can then be set to recharge batteries when prices are at a certain point.
Some smart chargers can even be set to prioritize electricity from renewable sources over those from gas, coal or nuclear power stations.
Multi-Source Power Integration
Where a household has multiple sources of power – the mains grid, wind turbines, solar panels, etc. – some Smart Chargers can be programmed to prioritize which power source they use.
A user could, for example, program the charger to use electricity from their solar panels if this is available but fall back to the mains grid when needed.
This again can result in major cost reductions.
Charger Management System Interface
There are a vast number of reasons why a user may want to get information or interact with a smart charger.
- to find out the current status of the charger
- to control the charger
- to program changes (such as timer settings)
- etc.
Some Smart Chargers include a user interface option. This could be a Smartphone app or a laptop/desktop program. In both cases the charger usually communicates via Bluetooth or Wi-Fi.
These interfaces vary greatly in complexity with the simpler ones simply displaying various pieces of information about the charger (charging / not charging; current rate of charge; etc.) to the highly complex which allow full control of the battery.
The Smart Charger and Smart Battery overlap
Where a compatible Smart Battery and Smart Charger are being used it may not always be clear which product is controlling what. For example the Smart Battery may be monitoring its own internal temperature and controlling the rate of charge while the Smart Charger controls how the electricity is being sourced.
If the combo has a user interface such as a smartphone app this may integrate data from both the charger and the battery making it nearly impossible to know whether it is the battery or the charger that is reporting certain data.
Summary
While this article defines what a Smart Charger can be it is important to remember that most smart chargers will only contain a few of these features, perhaps only one.
As such if you are looking to purchase a Smart Charger its important to check exactly which features it contains and how complex each of these is to be sure the charger will meet your needs.